The field of the present invention relates generally to electrically articulated devices using shape memory alloy (SMA) actuators. In particular, the field of the present invention relates to an improved electrically articulated multi-jointed manipulator which is adapted to be used as an endoscope, bronchoscope or a multi-jointed probe for robotic applications.
Conventional endoscopes are currently so-called "pull wire" devices which are used in conjunction with highly invasive surgery techniques. Typically, a conventional endoscope is insertable into a body cavity of a patient such as the colon, or bronchial tree (in the case of a bronchoscope) for performing a surgical operation. Conventional endoscopes or the like are simply pushed into a body cavity until they encounter an obstruction. Since conventional endoscopes and bronchoscopes are incapable of independent rotation when inserted into a body cavity, they presently cannot be maneuvered around an obstruction. Consequently, conventional endoscopes, bronchoscopes or like surgical implements pose serious risk of injury to delicate tissue. The invasive trauma to a patient caused by the use of a conventional endoscope, bronchoscope or the like is severe.
Attempts to use shape memory alloy (SMA) actuators to steer a conventional endoscope, bronchoscope, or the like until now have failed due to the large dimensions of the typical endoscope and the need for large current carrying feed wires to actuate such a large device. The large current carrying wires make a conventional SMA actuated device extremely bulky. The large wires thereby limit the total number of actuators and substantially reduce the maneuverability of an endoscope. Due to the need for large current carrying wires, conventional SMA endoscopes have not been built with more than two joints and are limited to two axes of actuation. Therefore, the conventional SMA actuated endoscopes presently have approximately the same capability of a pull wire endoscope. However, conventional SMA actuated endoscopes can cause an increase in invasive trauma which exceeds that of more pliable pull wire endoscopes which are simply pushed into place.
The large current carrying wires necessary to drive conventional SMA actuated endoscopes, bronchoscope, or the like also cause increased heat build up within the endoscope device. This has the disadvantage that heat must be dissipated through the body of the patient, causing the risk of burns. Accordingly, the invasive trauma caused by a conventional SMA actuated endoscope, bronchoscope, or the like is considerable and poses a serious risk of injury.
A further disadvantage of conventional pull wire endoscopes is that they are severely limited in their range of movement. The tip of such an endoscope is capable of being deflected in only a single plane.
Another problem with attempts to steer endoscopes by conventional SMA actuators is that a negative coefficient of expansion material such as a 50:50 or 49:51 formulation of titanium nickel (TiNi) is limited to a usable strain of only approximately 5% of its total length. Thus, it is impossible to obtain large or useful angular motion from a conventional SMA actuated joint.
Conventional SMA steerable devices operate by using a joint comprising two halves which are moved in different directions by antagonistically configured strips or actuator bands of 49:51 TiNi. Upon being resistively heated by application of an electric current, one of the TiNi bands contracts and imparts movement to one half of the joint. However, because conventional SMA actuators configured as negative coefficient of expansion materials are limited to a usable strain of only 5% of total length, they must be made extremely long in order to derive useful movement. This has the disadvantage of increasing the size of the joint, thereby increasing bulk and the risk of invasive trauma.
Since SMA actuators are current driven devices, the large size of a conventional SMA actuator also necessitates a large diameter wire for providing the activation current for resistively heating the joint to its activation threshold. This also creates undesirable bulk and problems of heat dissipation as set forth above.
Conventional means for actively steering a device such as an endoscope for performing dexterous surgical maneuvers suffer from a further disadvantage of torsional rigidity. Presently, the body of an endoscope must be rotated by hand about the longitudinal axis to cause the tip of the endoscope to reach a different point within the patient. Conventional endoscopes therefore must be maintained torsionally rigid over their entire length. When a torsionally rigid endoscope is rotated in order to move the tip in a desired direction, extreme trauma to tissue can result since the entire torsionally rigid body of the endoscope also must be rotated.
The torsionally stiff body of a conventional endoscope, when positioned in a convoluted path, places large incidental forces on the walls of a vessel through the action of making a rotation. There are two contributions to the incidental forces. The first results from moving a convoluted shape in a rotation. The other contribution to the incidental force results from the inherent stiffness of a conventional endoscope. What is needed is an endoscope or multi-jointed probe which has the advantage of being extremely maneuverable and pliable, but at the same time can be rotated and execute highly dexterous maneuvers in three dimensions.
What is needed is a new type of endoscope which can perform highly dexterous maneuvers in three dimensions without built in torsional stiffness. Such an endoscope would be steerable without torsional rigidity to perform complex maneuvers and would be minimally invasive.
What is also needed is an improved method and apparatus for actively steering a surgical device such as an endoscope, bronchoscope or the like with a minimum of invasive trauma to a patient and which would provide tactile feedback to the operating physician without torsional rigidity.
It would also be highly desirable to provide an improved SMA actuator joint with a greater range of motion, while at the same time minimizing the size of such a joint. Such an improved SMA actuator joint would operate on low current to minimize heat dissipation and also would be more maneuverable due to its smaller size. What is also needed is an improved low current SMA actuator joint which would capable of imparting sufficient torque to an endoscope, bronchoscope or the like to provide extreme dexterity and maneuverability over a wide range of motion. The elimination of bulky current carrying feed wires would provide a significant advance in minimally invasive surgical procedures over conventional endoscopes.
What is also needed is an improved control system for providing visual feedback for accurately positioning and steering an endoscope or similar surgical device within a patient. Such a control system would advantageously be capable of performing highly dexterous maneuvers in three dimensions.